The world's smallest known surviving baby has made her first public appearance at a US hospital, alongside her slightly larger twin sister.

Rumaisa Rahman weighed just 244g (8.6 ounces) when she was born prematurely in Chicago on 19 September - less than a can of soft drink.

Rumaisa's Indian-born parents hope to take her and sister Hiba to their home in the city by early next month.

"It's a blessing, it's a great blessing," said the girls' mother.

Doctors had waited to announce the girls' birth until after it was clear they were healthy and were nearly ready to leave the hospital.

"They're maintaining their temperature, they don't need an incubator.... They're normal babies," said Dr William MacMillan at Loyola University Medical Center.

Rumaisa was about the size of a mobile phone when she was born, 15 weeks before her due date. She still only weighs 1.18kg (2 pounds 10 ounces).

Blood pressure

Hiba weighed 563g (1 pound 4 ounces) at birth, and has now reached 2.25kg (5 pounds). She may leave the hospital by the end of the month, but Rumaisa will probably have to stay until early January.

Their mother, Mahajabeen Shaik, 23, developed severe pre-eclampsia, a disorder characterised by high blood pressure and other problems, during pregnancy. She and her husband, Mohammed Abdul Rahman, 32, are originally from Hyderabad, India.

The twins were delivered by Caesarean section at 25 weeks and six days.

Both girls have undergone laser surgery to correct vision problems that are common in premature babies.